As far as ships are concerned, current practice is to dump liquid and solid wastes in mid-ocean without any treatment. This is reasonably acceptable for bio-degradeable materials but the increasing use of non-degradeable materials such as plastics means that this is a source of pollution due to floating debris. Ships are prohibited from discharging untreated wastes in ports, harbours and coastal waters and so storage tanks are usually provided in which the wastes are stored for discharge in deeper waters. This solution is unlikely to be acceptable in the future as pollution control measures cover a greater proportion of coastal and enclosed areas because of the excessive size of the storage tanks required.
Sewage and domestic waste can be treated by biological degradation, but this is susceptible to interference by the presence of salt water and this implies, in a marine environment, an unacceptable degree of reliability. In addition, the biological degradation of these wastes leads to the formation of a treated liquid effluent and an associated quantity of sludge consisting of non-degradeable residues and micro-organisms. This sludge requires to be stored for subsequent treatment or discharge in ocean waters. Treatment of wastes by chemical means is also available but the cost of dosing the total waste in this manner is expensive.
The increasing use of plastic non-degradeable materials for packaging, disposable utensils and containers constitutes a major pollution threat in that many of these articles are of low density and, if discharged overboard, will remain floating for an indefinite period of time. There is growing disquiet at the accumulation of this debris in ports, harbours and beaches adjacent to sea lanes, and pressure is mounting for legislation to prohibit these discharges, similar to that which prohibits discharge of oily wastes into water.
Many, if not all, of these considerations also apply to the problems of waste disposal at remotely situated inland sites.
It is therefore, an object of this invention to provide a waste treatment plant which can accept all such forms of waste for disposal in a way which reduces or avoids pollution.